The development of optical elements, including ophthalmic lenses, sunglass lenses and other optical lenses, which are manufactured from plastic materials has also lead to the development of a variety of coatings for use on the optical elements. For example, coatings that provide an increase in abrasion resistance or a decrease in the amount of reflected light have been developed.
Commonly, thermoset plastic materials such as CR-39, Finalite (a registered trademark of Sola International Inc.) and Spectralite (a registered trademark of Sola International Inc.) are used in the manufacture of optical elements such as ophthalmic lenses. A common thermoplastic material that is used in the manufacture of optical elements is the polycarbonate of bisphenol A. Other plastics that have also been used include a variety of commercial thiourethane materials. However it has been found that, in use, ophthalmic lenses and other optical elements formed from these plastics tend to be more easily scratched or abraded on external surfaces than the more traditional glass counterparts.
To overcome this problem, abrasion resistant coatings for plastic optical elements have been developed. Usually, a coating material (typically a monomer) is coated onto outer surfaces of the optical element and the monomeric coating material is then cured to form a coating that is more resistant to abrasion than the plastic material from which the optical element is formed. This practice is commonly referred to as the ‘hard coating’ of a lens.
With many hard coating processes a primer coating is sometimes required to provide sufficient adhesion of the coating to the optical element and this contributes to the cost of manufacture. Alternatively, primerless coatings are available however they typically do not provide a sufficient level of abrasion resistance.
In order to overcome some of the manufacturing costs associated with hard coating an uncoated optical element the process of in-mould coating has been developed. In-mould coating involves coating an inner mould surface with a coating composition prior to casting or moulding an optical element. Unfortunately, in most cases the materials used to form coatings in these processes do not provide a sufficient level of abrasion resistance.
The present invention aims to provide a coating composition and a method of coating an optical element, such as an ophthalmic lens, that ameliorates any one or more of the problems with existing abrasion resistant coatings and techniques for forming abrasion resistant coatings on optical elements. Alternatively, the present invention aims to provide an alternative to existing abrasion resistant coatings and techniques for forming abrasion resistant coatings on optical elements.